Research on the electrical characteristics of an organic thin-film field-effect transistor based on alternating-current resistance

In this article, an organic thin-film field-effect transistor （OTFFET） with top-gate and bottom-contact geometry based on pentacene as the active layer is fabricated. The experimental data of the I-V are obtained from the OTFFET device. The alternating-current （AC） resistance value of the OTFFET device is calculated using the derivation method from the experimental data, and the AC resistance trend curves of the OTFFET device are obtained with the region fitting method. We analyse the characteristics of the OTFFET device with an AC resistance trend curve. To discover whether it has a high resistance, it is proposed to judge the region of the source/drain voltage （VDs） less than the transition voltage, thereby determining whether the contact between the metal electrode and the organic semiconductor layer of the OTFFET device is Ohmic or non-Ohmic. The theoretical analysis shows that the field-effect mobility and the AC resistance are in reverse proportion. Therefore, we point out that reducing AC resistance is necessary if field-effect mobility is to be improved.

Study on characteristics of a double-conductible channel organic thin-film transistor with an ultra-thin hole-blocking layer

The properties of top-contact organic thin-film transistors （TC-OTFTs） using ultra-thin 2, 9-dimethyl-4, 7- diphenyl-1, 10-phenanthroline （BCP） as a hole-blocking interlayer have been improved significantly and a BCP interlayer was inserted into the middle of the pentacene active layer. This paper obtains a fire-new transport mode of an OTFT device with double-conductible channels. The accumulation and transfer of the hole carriers arc limited by the BCP interlayer in the vertical region of the channel. A huge amount of carriers is located not only at the interface between pentacene and the gate insulator, but also at the two interfaces of pentacene/BCP interlayer and pentacene/gate insulator, respectively. The results suggest that the BCP interlayer may be useful to adjust the hole accumulation and transfer, and can increase the hole mobility and output current of OTFTs. The TC-OTFTs with a BCP interlayer at VDS = --20 V showed excellent hole mobility μFE and threshold voltage VTH of 0.58 cm^2/（V-s） and -4.6 V, respectively.

Organic thin-film transistors and related devices in life and health monitoring

The early determination of disease-related biomarkers can significantly improve the survival rate of patients.Thus,a series of explorations for new diagnosis technologies,such as optical and electrochemical methods,have been devoted to life and health monitoring.Organic thin-film transistor(OTFT),as a state-of-the-art nano-sensing technology,has attracted significant attention from construction to application owing to the merits of being label-free,low-cost,facial,and rapid detection with multi-parameter responses.Nevertheless,interference from non-specific adsorption is inevitable in complex biological samples such as body liquid and exhaled gas,so the reliability and accuracy of the biosensor need to be further improved while ensuring sensitivity,selectivity,and stability.Herein,we overviewed the composition,mechanism,and construction strategies of OTFTs for the practical determination of disease-related biomarkers in both body fluids and exhaled gas.The results show that the realization of bio-inspired applications will come true with the rapid development of high-effective OTFTs and related devices.

Interfacial molecular screening of polyimide dielectric towards high-performance organic field-effect transistors

The compatibility of the gate dielectrics with semiconductors is vital for constructing efficient conducting channel for high charge transport.However,it is still a highly challenging mission to clearly clarify the relationship between the dielectric layers and the chemical structure of semiconductors,especially vacuum-deposited small molecules.Here,interfacial molecular screening of polyimide(Kapton)dielectric in organic field-effect transistors(OFETs)is comprehensively studied.It is found that the semiconducting small molecules with alkyl side chains prefer to form a high-quality charge transport layer on polyimide(PI)dielectrics compared with the molecules without alkyl side chains.On this basis,the fabricated transistors could reach the mobility of 1.2 cm^(2) V^(−1)s^(−1) the molecule with alkyl side chains on bare PI dielectric.What is more,the compatible semiconductor and dielectric would further produce a low activation energy(E_(A))of 3.01 meV towards efficient charge transport even at low temperature(e.g.,100 K,0.9 cm^(2) V^(−1)s^(−1)).Our research provides a guiding scheme for the construction of high-performance thin-film field-effect transistors based on PI dielectric layer at room and low temperatures.

Diketopyrrolopyrrole-based Conjugated Polymers as Representative Semiconductors for High-Performance Organic Thin-Film Transistors and Circuits

Since the first report of diketopyrrolopyrrole(DPP)-based conjugated polymers for organic thin-film transistors(OTFTs),these polymers have attracted great attention as representative semiconductors in high-performance OTFTs.Through unremitting efforts in molecular-structure regulation and device optimization,significant mobilities exceeding 10 cm2·V–1·s–1 have been achieved in OTFTs,greatly promoting the applied development of organic circuits.In this review,we summarize our progress in molecular design,synthesis and solution-processing of DPP-based conjugated polymers for OTFT devices and circuits,focusing on the roles of design strategies,synthesis methods and processing techniques.Furthermore,the remaining issues and future outlook in the field are briefly discussed.

3-Methylcyclohexanone Processed n-Channel Organic Thin-Film Transistors Based on a Conjugated Polymer Synthesized by Direct Arylation Polycondensation

The solubility of a direct arylation polycondensation(DArP)synthesized conjugated polymer,i.e.,poly(3,6-bis(furan-2-yl)-2,5-bis(4-tetradecyloctadecyl)-pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-1,2-bis(3,4-d ifl uorothien-2-yl)ethene)(PFuD PP-4FTVT),in variou s organic solvents was studied.The polymer is soluble in 3-methylcyclohexanone(3-MC),a green solvent from peppermint oil,besides other solvents such as anisole,cyclopentyl methyl ether(CPME)and o-dichlorobenzene(o-DCB),etc.Based on the Hansen solu bility parameters(HSP)analysis,3-MC is identified as a"marginal solvent"of PFuDPP-4FTVT.The morphology of the spin-coated films with 3-MC as the solvent strongly correlated with the solution preparation conditions.With a 3-MC solution aged for 3 h at 70℃,n-channel organic thin-film transistors(OTFTs)with electron mobility(μe)above 1 cm^(2)·V^(-1)·s^(-1) and current on/off ratio(Ion/Ioff)higher than 105 were fabricated by spin-coating.This is the first report on high mobility conjugated polymers for OTFTs processible with natu rally occurred green solvent.

Modulating contact properties by molecular layers in organic thin-film transistors

Advanced organic devices and circuits demand both ultrahigh charge carrier mobilities and ultralow-resistance contacts.However,due to a larger access resistance in staggered organic thin-film transistors(OTFTs),the achievement of ultralow contact resistance(Rc)is still a challenge.The modulation of contact resistance by molecular layers near the interface has been rarely reported.Here,we demonstrate that fewlayer organic single crystals are grown on hafnium oxide(HfO_(2))by solution-shearing epitaxy.We utilize these organic crystals to fabricate bottom-gate staggered OTFTs with different contact processes.The results show that the contact properties of OTFTs are obviously modulated by crystal layers.The tri-layer(3L)evaporated-Au C10-DNTT OTFTs exhibit optimal electrical performance,including ultralow Rc of 5.6Ω⋅cm,recorded transfer length of 0.4μm,field-effect mobility over 14 cm^(2)V^(−1)s^(−1),threshold voltage lower than 0.3 V,and long-term air stability over 8 months.The main cause is that the metal atoms can penetrate into the charge transport layer,with damage-free,in 3L evaporated-Au OTFTs;nevertheless,it cannot be realized in other cases.Due to layer stacking of conjugated molecules and polymers,our strategy can efficiently modulate the contact resistance to aid the development of highperformance organic devices and circuits.

多壁碳纳米管/α-六噻吩双层OTFT气体传感器的制备及特性分析

以多壁碳纳米管（multi-walledcarbonnanotubes,MWCNTs）和α-六噻吩（α-sexithiophene,α-6T）双层膜作为有源层,二氧化硅（SiO2）为绝缘层,钛/金（Ti/Au）作为电极,制备了沟道宽长比为640的有机薄膜晶体管（organicthin-filmtransistors,OTFT）气体传感器.测试了该传感器对痕量二氧化氮（NO2）气体的实时响应特性,并分析了NO2 气体对OTFT传感器阈值电压、载流子迁移率等多参数的影响.研究结果表明,基于MWCNTs/α-6T 的OTFT器件有较好的电学特性,载流子迁移率为3.0×10-2cm2/V·s;OTFT传感器对NO2 气体具有较高的响应率,响应和恢复时间短,能检测（0.2~1）×10-6 的痕量NO2 气体,且具有良好的重复性;同时可以利用阈值电压和载流子迁移率等多参数来表征响应结果.形貌分析结果表明双层敏感膜的特殊形貌有利于提高器件的气敏性能.

喷墨打印C8-BTBT薄膜中的衬底效应及其OTFT器件

以喷墨打印制备的共轭有机小分子2,7-二辛基[1]苯并噻吩并[3,2-b]苯并噻吩(C8-BTBT)作为有机薄膜晶体管(OTFT)的有源层,分别采用紫外臭氧处理、旋涂聚(4-乙烯基苯酚)(PVP)薄膜、自组装苯乙基三氯硅烷(PETS)单分子层和苯基三氯硅烷(PTS)单分子层四种衬底修饰方法,分析有机小分子薄膜生长过程中的衬底效应,及其对OTFT器件性能的影响。其中PVP或PETS修饰衬底具有疏水及低表面粗糙度的特性,在其上喷墨打印沉积的C8-BTBT单线条薄膜具有均匀性好、覆盖率高且有序堆积的结晶形貌,基于这种高质量薄膜制备的OTFT器件性能最优,饱和场效应迁移率达到1 cm2·V-1·s-1左右,开关比超过106。结果表明,对打印衬底进行疏水性处理及降低表面粗糙度是制备高性能共轭小分子OTFT器件的有效途径。

绝缘修饰层及其厚度对喷墨打印OTFT的影响

通过在底栅顶接触的喷墨打印有机薄膜晶体管的Si O2表面采用原子层沉积方式制备薄层的Al2O3修饰层,并与未修饰前进行比较,发现有源层在ALD-Al2O3修饰后的Si O2表面接触角大大变小,且喷墨打印的有源层线条变粗。而随着ALD-Al2O3修饰层厚度的增加,Si O2表面粗糙度变大。通过测试其电学性能,发现ALD-Al2O3修饰层厚度为1 nm时,OTFT的性能最好,与未修饰前相比,其迁移率提高了近8倍,而开关比提高约4个数量级。

有源层厚度对CuPc-OTFT器件性能的影响

研究了不同厚度有源层的顶电极CuPc OTFT器件的电学特性。发现器件的性能与有源层厚度有依赖关系,其中,有源层厚度为20nm的器件性能最好。在有源层厚度大于20nm时,有源层厚度的增大不但分去一部分栅电压而且还增大了源、漏电极的接触电阻,从而不利于器件性能的提高。但当有源层厚度小于20nm以后器件的性能开始降低。我们认为当有源层厚度降低到一定程度时,有源层上表面的表面态会使有机材料的隙态浓度增加从而对沟道载流子迁移率产生不良影响以及使器件的阈值电压增大。

C8 BTBT薄膜结晶形貌及OTFT器件性能研究

以p型共轭有机小分子2,7二辛基[1]苯并噻吩并[3,2‐b]苯并噻吩(C8‐BTBT)作为底栅顶接触有机薄膜晶体管(OTFT)的有源层,采用浸渍提拉法、喷墨打印法和真空蒸镀法三种制备工艺,探究半导体薄膜载流子迁移率与结晶形貌的关系,发现不同工艺下有机小分子呈现出不同的生长行为和结晶情况,在很大程度上决定了OTFT器件性能的优劣;此外,通过XRD分析研究了退火处理对C8‐BTBT结晶的影响。结果表明,真空蒸镀制备的薄膜具有更高的结晶度、衬底覆盖率高,并且呈现出SK(Stranski‐Krastanov)模式的结晶生长特征,相应器件中陷阱密度最低,迁移率高达5.44 cm^2·V^-1·s^-1,开关比超过106;且退火处理会严重破坏C8‐BTBT薄膜的结晶。因此,控制半导体层的生长行为,提升半导体层的覆盖率和结晶度是制备高性能共轭小分子OTFT器件的有效途径。

PMMA栅绝缘层表面形貌对并五苯OTFT性能的影响

影响有机薄膜晶体管(organic thin-film transistor,OTFT)器件性能的主要因素中,栅绝缘层表面形貌特性和薄膜厚度等有着非常关键的作用,会直接影响有源层材料的分子排列方式和整个器件的性能。以氧化铟锡(ITO)导电薄膜玻璃为衬底材料,采用溶液旋涂的工艺制备聚合物聚甲基丙烯酸甲酯(PMMA)有机绝缘层,采用真空蒸镀的方法制备并五苯有源层及源-漏银电极。通过对比不同退火条件下PMMA绝缘栅层表面形貌及粗糙度,制备适合有源层生长的绝缘层表面,得到较好的PMMA栅绝缘层/并五苯有源层界面接触。实验表明,PMMA栅绝缘层经退火后所制备的器件场效应迁移率提高到2.52×10-3 cm2/(V·s),阈值电压降低到-11.5 V,获得了性能较好的OTFT。

简化DG OTFT结构对模拟精度的影响

使用atlas软件模拟了两种器件结构的电学特性(阈值电压、开关电流比、亚阈值斜率等),其中一种是工艺制造的DG OTFT实际结构,另一种是模拟研究器件电学特性时常采用的DG OTFT简化结构。研究发现实际结构的输出电流会随着源漏电极厚度的增加而加大,而模拟中常采用的简化结构由于忽略了电极位置对载流子注入面积及有源层内电势分布的影响,从而低估了实际器件的输出电流大小。

Preparation of organic thin-film field effect transistor

The organic thin-film field effect transistor was prepared through vacuum deposition by using teflon as dielectric material. Indium-tin-oxide acted as the source and drain electrodes. Copper phthalocyanine and teflon were used as the semiconductor layer and dielectric layer, respectively. The gate electrode was made of Ag. The channel length between the source and drain was 50μm. After preparing the source and drain electrodes by lithography, the copper phthalocyanine layer, teflon layer and Ag layer were prepared by vacuum deposition sequentially. The field effect electron mobility of the device reached 1.1×10-6 cm2/(V·s), and the on/off current ratio reached 500.

Chlorinated Conjugated Polymer Based on Chlorine- and Cyano-substituted (E)-1,2-Di(thiophen-2-yl)ethane for Ambipolar and n-Type Organic Thin-film Transistors

Chlorinated conjugated polymers are rarely reported in ambipolar and n-type organic thin-film transistors(OTFTs),mainly due to the lack of chlorinated strong electron-deficient building blocks.Herein,we report three new chlorine(Cl)-and cyano(CN)-substituted(E)-1,2-di(thiophen-2-yl)ethane building blocks and their copolymers P2Cl1CNTVT-DPP,P4Cl1CNTVT-DPP and P2Cl2CNTVT-DPP.

Acceptor-Donor-Acceptor Conjugated Oligomers Based on Diketopyrrolopyrrole and Thienoacenes with Four, Five and Six Rings for Organic Thin-film Transistors

Three acceptor-donor-acceptor （A-D-A） conjugated oligomers, i.e., O1, 02 and 03, have been synthesized using diketopyrrolopyrrole （DPP） as an electron-acceptor unit, and naphtho[1,2-b：5,6-b＇]dithiophene （NDT）, anthra[1,2-b：5,6- b＇]dithiophene （ADT） or dithieno[3,2-b：Y,2＇-b＇]naphtbo[1,2-b：5,6-b＇]dithiophene （DTNDT） as electron-donor unit. These oligomers exhibit identical highest occupied molecular orbital （HOMO） and lowest unoccupied molecular orbital （LUMO） energy levels, which were ca. -5.1 and -3.3 eV, respectively. Upon thermal annealing, all three oligomers formed thin films with ordered microstructures, and their organic thin film transistors （OTFTs） exhibited p-type transport behavior. The mobility was increased with an extension of the size of D-units. 03 showed the best OTFT performance with the mobility of up to 0.20 cm2·V-1 ·s-1. The film quality of 03 was improved by adding 1 wt% poly（methylmethacrylate） （PMMA）. In consequence, the mobility of the O3-based devices was further enhanced to 0.30 cm2·V-1 ·s-1.

Printed unmanned aerial vehicles using paper-based electroactive polymer actuators and organic ion gel transistors

We combined lightweight and mechanically flexible printed transistors and actuators with a paper unmanned aerial vehicle(UAV)glider prototype to demonstrate electrically controlled glide path modification in a lightweight,disposable UAV system.The integration of lightweight and mechanically flexible electronics that is offered by printed electronics is uniquely attractive in this regard because it enables flight control in an inexpensive,disposable,and easily integrated system.Here,we demonstrate electroactive polymer(EAP)actuators that are directly printed into paper that act as steering elements for low cost,lightweight paper UAVs.We drive these actuators by using ion gel-gated organic thin film transistors(OTFTs)that are ideally suited as drive transistors for these actuators in terms of drive current and frequency requirements.By using a printing-based fabrication process on a paper glider,we are able to deliver an attractive path to the realization of inexpensive UAVs for ubiquitous sensing and monitoring flight applications.

有机薄膜晶体管气体传感器的研究进展

重点介绍了电子科技大学电子薄膜与集成器件国家重点实验室在国家自然科学基金资助下开展的有机薄膜晶体管(OTFT)气体传感器方面的研究进展。制备了酞菁铜(CuPc)薄膜为有源层的底栅底接触式结构的有机薄膜晶体管,对器件的制备工艺和结构参数进行了优化,研究了其对H_2S气体的敏感特性。同时制备了P3HT-ZnO纳米棒的复合薄膜、P3HT单层薄膜、P3HT-MoS_2分层膜和复合膜的有机薄膜晶体管气体传感器,系统地分析了OTFT器件的电学性能和气敏特性。

基于聚噻吩/聚己内酯共混物的有机薄膜晶体管

选择聚3-己基噻吩(P3HT)/聚己内酯(PCL)双晶共混体系制备了不同配比的共混物有机薄膜晶体管。电学性能研究发现,随着共混物中P3HT含量降低,薄膜晶体管的场效应迁移率、开关电流比和阈值电压等性能缓慢降低。当P3HT质量分数为40%时,共混物薄膜仍具有较好的场效应性能,迁移率为0.008 cm2.V-1.s-1,开关电流比为5×103,阈值电压为45.5 V。原子力显微镜测试结果表明:共混物成膜时发生明显的垂直相分离,在界面处形成连续的半导体层,有利于载流子传输。